Ensure that inverse associations are set before running callbacks

If a parent association was accessed in an `after_find` or
`after_initialize` callback, it would always end up loading the
association, and then immediately overwriting the association we just
loaded. If this occurred in a way that the parent's `current_scope` was
set to eager load the child, this would result in an infinite loop and
eventually overflow the stack.

For records that are created with `.new`, we have a mechanism to
perform an action before the callbacks are run. I've introduced the same
code path for records created with `instantiate`, and updated all code
which sets inverse instances on newly loaded associations to use this
block instead.

Fixes #26320.

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index a6615f3774..a04ef2e263 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -63,10 +63,10 @@ module ActiveRecord
       #
       # See <tt>ActiveRecord::Inheritance#discriminate_class_for_record</tt> to see
       # how this "single-table" inheritance mapping is implemented.
-      def instantiate(attributes, column_types = {})
+      def instantiate(attributes, column_types = {}, &block)
         klass = discriminate_class_for_record(attributes)
         attributes = klass.attributes_builder.build_from_database(attributes, column_types)
-        klass.allocate.init_with("attributes" => attributes, "new_record" => false)
+        klass.allocate.init_with("attributes" => attributes, "new_record" => false, &block)
       end
 
       private